Derivative Instruments and Hedging Activities (Outstanding Derivative Instruments) (Details) (USD $)		1 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2012 Designated as Hedging Instrument [Member] Interest Rate Contract [Member]	Sep. 30, 2013 Designated as Hedging Instrument [Member] Forward Contract Power [Member] MWh	Dec. 31, 2012 Designated as Hedging Instrument [Member] Forward Contract Power [Member] MWh	Sep. 30, 2013 Designated as Hedging Instrument [Member] DP&L [Member] Forward Contract Power [Member] MWh	Dec. 31, 2012 Designated as Hedging Instrument [Member] DP&L [Member] Forward Contract Power [Member] MWh	Sep. 30, 2013 Not Designated as Hedging Instrument [Member] Commodity Contract - FTR [Member] MWh	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Commodity Contract - FTR [Member] MWh	Sep. 30, 2013 Not Designated as Hedging Instrument [Member] Commodity Contract - Heating Oil [Member] gal	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Commodity Contract - Heating Oil [Member] gal	Sep. 30, 2013 Not Designated as Hedging Instrument [Member] Forward Contract Power [Member] MWh	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] Forward Contract Power [Member] MWh	Sep. 30, 2013 Not Designated as Hedging Instrument [Member] DP&L [Member] Commodity Contract - FTR [Member] MWh	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] DP&L [Member] Commodity Contract - FTR [Member] MWh	Sep. 30, 2013 Not Designated as Hedging Instrument [Member] DP&L [Member] Commodity Contract - Heating Oil [Member] gal	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] DP&L [Member] Commodity Contract - Heating Oil [Member] gal	Sep. 30, 2013 Not Designated as Hedging Instrument [Member] DP&L [Member] Forward Contract Power [Member] MWh	Dec. 31, 2012 Not Designated as Hedging Instrument [Member] DP&L [Member] Forward Contract Power [Member] MWh
Purchase of Units Derivative Instruments Financial Transmission Rights						10,700	6,900					10,700	6,900
Purchase of Volume Units Derivative Instruments Heating Oil Futures								1,638,000	1,764,000					1,638,000	1,764,000
Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge		421,600	1,021,000	421,600	1,021,000
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge		(4,719,400)	(2,197,900)	(4,719,400)	(2,197,900)
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged										2,653,300	2,510,700					2,624,600	2,296,600
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged										(7,012,500)	(4,760,400)					(7,041,300)	(4,760,400)
Purchase of Derivative Instruments Interest Rate Swaps	$ 160,000,000
Derivative, Nonmonetary Notional Amount MWh		(4,297,800)	(1,176,900)	(4,297,800)	(1,176,900)	10,700	6,900			(4,359,200)	(2,249,700)	10,700	6,900			(4,416,700)	(2,463,800)
Derivative, Nonmonetary Notional Amount Volume								1,638,000	1,764,000					1,638,000	1,764,000
Notional Amount of Derivatives	$ 160,000,000